1. Field of the Invention
This invention relates to multiplexing type circuits, and more particularly, to such a circuit wherein selected input and output leads thereof can be disconnected.
2. Description of the Prior Art
In a typical prior art multiplexing circuit (FIG. 1 at 10), the circuit 10 can include a plurality of circuit portions 12, 14, 16, each having one or more input leads 18, 20, 22 and one or more output leads 24, 26, 28 connected thereto. The output leads 24, 26, 28 are in turn connected to an overall circuit output lead 30, and control leads 32, 34, 36 are individually connected to respective circuit portions 12, 14, 16 so that the user of the circuit 10 may choose which circuit portion he wishes to have in operation, and then apply input signals thereto and receive output signals therefrom to be applied to the overall output lead 30 of the circuit.
In this manner, the functions of each circuit portion can be applied individually as needed.
Presently, it has been found desirable to initially provide a multiplexing circuit which includes multiple circuit portions only one of which is to be chosen for ongoing future use, while the others may be initially included in but eventually excluded from the overall circuit. In such case, it may be desirable to test each of the circuit portions individually to determine its functionality (by application of high and low signals to appropriate circuit terminals in accordance with an established test program, as is well known), and then to choose the one which most optimally fits the needs of the user.
The multiplexing circuit of the type shown in FIG. 1 lends itself to that testing. However, such a circuit, subsequent to testing, includes the undesired circuit portions as part of the overall circuit, resulting in excessive use of power and a higher degree of loading on the previous and following circuits than is optimum.